The invention relates to a device and a process for controlling a person protection system of a motor vehicle having a sensor system which, for the detection of an object colliding with the motor vehicle, includes a hose that is arranged along the width of a body section of the motor vehicle and is closed off by way of a pressure sensor on at least one of its ends. The hose is arranged in the motor vehicle such that, in the event of an impact of the object, a pressure change is caused in the hose interior as a result of the deformation of the hose and can be detected and processed as a pressure signal of the at least one pressure sensor by an evaluating unit connected with the at least one pressure sensor.
Such devices are normally provided in front bumpers of motor vehicles. The sensor system has the purpose of detecting the impact of a pedestrian and, as a supplement to a passive energy absorption by an impact-absorbing material integrated in the bumper, initiating additional active protective measures for the pedestrian or bicyclist. These measures may consist, for example, of raising an engine hood or other flap. This helps prevent the hit pedestrian or bicyclist from being seriously injured or killed by the impact on the engine hood and the engine block situated underneath. Valuable protective space is created by the additional centimeters of distance between the engine hood and engine block, which considerably alleviates the results of an accident.
So far, optical waveguides or acceleration sensors have been used as sensors for detecting a pedestrian impact. In the meantime, so-called pressure hose sensors are known, where, as a rule, two air pressure sensors are mutually connected by way of the hose. The hose as well as the pressure sensors are integrated in the so-called front end of the motor vehicle between a supporting cross member and a plastic covering of the bumper in an extruded plastic foam. In this case, the hose is placed in the bumper of the motor vehicle over the entire width of the vehicle. The hose is situated directly behind a block consisting of the plastic foam which is installed in the bumper as an energy absorbing device. The pressure sensors arranged at the two ends of the pressure hose filled with air are standardized pressure sensors which can also be used, for example, for activating airbags of the motor vehicle in the event of a side impact. The bumper is deformed when the motor vehicle collides with an obstacle. The corresponding deformation leads to a pressure change in the hose, which pressure change is detected by the pressure sensors. The electrical signals are evaluated by an evaluating unit, for example, an airbag control device. The type of the collision can be calculated by way of crash algorithms in the evaluating unit and speed information. By means of signal traveling times, conclusions can also be drawn on the impact location; for example, whether the impact was at the front right or more in the vehicle center. As a function of the signal pattern, suitable protection systems can then be activated in time.
The sensor system has to reliably recognize a collision between a vehicle and a pedestrian, irrespective of whether the person involved in the accident is a small child or a grown man. Furthermore, the sensors should determine in a highly reliable manner whether a so-called “no-fire” case exists in which the protection systems should absolutely not be triggered. Such events are, for example, the touching of a curb by means of the bumper or a collision with a small animal.
The pressure hose sensor system offers good performance as well as advantages for the mechanical integration in a motor vehicle. In addition, it is very cost-effective compared with other known sensor systems. A disadvantage of pressure hose sensor systems consists of the fact that, so far, it has not been possible to completely test these systems electrically via a diagnosis with respect to their functioning. Only an electrical testing of the pressure sensors is possible, whereas the pressure hose and its connection to the pressure sensors cannot be tested in this manner with respect to the appropriate functioning. A faulty condition of the pressure hose may be caused, for example, by a marten bite. Likewise, a pressure sensor could become detached from the hose in the course of the service life of the motor vehicle. This disadvantage stands in the way of a rapid propagation of the system.
It is an object of the present invention to provide a device and a process which permit the complete diagnosis of a passenger protection system based on a pressure hose sensor system.
This and other objects are achieved by a device and process for controlling a person protection system of a motor vehicle having a sensor system which, for the detection of an object colliding with the motor vehicle, comprises a hose that is arranged along the width of a body section of the motor vehicle and is closed off by means of a pressure sensor on at least one of its ends. The hose is arranged in the motor vehicle such that, in the event of an impact of the object, a pressure change is caused in the hose interior as a result of the deformation of the hose and can be detected and processed as a pressure signal of the at least one pressure sensor by an evaluating unit connected with the at least one pressure sensor. The evaluating unit for diagnosing the sensor system is constructed for detecting vibrations originating from the motor vehicle during the driving and testing operation and coupled into the hose, which vibrations result in pressure fluctuations in the hose interior which are lower than a pressure fluctuation caused by an impacting object and for evaluating these vibrations for a predefined time period.
The invention further provides a process for controlling a person protection system of a motor vehicle having a sensor system of the above-described type, wherein the evaluating unit for diagnosing the sensor system detects vibrations originating from the motor vehicle during the driving and testing operation and coupled into the hose, which vibrations result in pressure fluctuations in the hose interior which are lower than a pressure fluctuation caused by an impacting object and evaluates these vibrations for a predefined time period.
The invention is based on the consideration that a pressure hose sensor system like the one described in the background above is no longer accessible from the outside after it is integrated into the motor vehicle. Although the pressure sensor or sensors can be electrically tested with respect to an appropriate operability in a conventional manner, the (pressure) hose connected with the pressure sensor or sensors is not accessible for such a diagnosis. In particular, a visual inspection of the pressure hose can also not take place because of its special arrangement inside or behind a block made of plastic foam, which is installed in a bumper as an energy absorber.
According to an aspect of the invention, a diagnosis of the pressure hose, including its linkage to the at least one pressure sensor and thereby of the sensor system as a whole, is carried out in an indirect manner. As the driver is operating the motor vehicle, vibrations are transmitted to the motor vehicle during every movement of the vehicle. These vibrations are coupled into the sensor system including the hose partially also as very slight interferences. In order to obtain information concerning the operability of the sensor system, the interferences coupled into the sensor system are evaluated. Since these interferences are very slight and can therefore not provide any information concerning the operability of the sensor system within a short time period, the evaluation takes place over an extended time period, for example, several minutes, hours or even days.
For diagnosing the sensor system, it can, for example, be examined by the evaluating unit whether certain threshold values for the pressure fluctuation occur in a predefined number within the predefined time period. For example, the occurrence of a comparatively high pressure fluctuation (which, however, would then still be considerably lower than the pressure fluctuation caused by an impacting object) may indicate the appropriate operability of the sensor system. Such a comparatively high pressure fluctuation may occur, for example, when driving through a pothole. When the motor vehicle is moving along a road with a good even surface, under certain circumstances, no significant pressure fluctuations may be detected for a fairly long time period. During this time period, the occurrence of a plurality of comparatively small pressure fluctuations may provide information on the operability of the sensor system.
On the whole, corresponding information concerning the operability of the hose or of the sensor system can be written, for example, into a memory of the evaluating unit. If the state of the sensor system corresponds to a defined fault case, corresponding information can be emitted, for example, by way of a control light or a display of the motor vehicle. The information optionally stored in the memory of the evaluating unit can also be read out of the evaluating unit and be evaluated within the scope of a service shop visit.
It was found to be sufficient for the pressure fluctuations caused by the driving or testing operation to amount to not more than one tenth of the pressure fluctuation caused by an impacting object. In this manner, it can also be ensured that a sufficiently large interval exists between a pressure fluctuation for the verification of the operability of the sensor system and an actual triggering case. On the other hand, pressure fluctuations in the above-mentioned range are sufficient for a differentiation of the latter from a statistical noise of the pressure sensors. Depending on the further development of the pressure hose, the maximum for the pressure fluctuation may also be selected to be different.
Furthermore, it is advantageous to fasten a source of interference to the hose or to arrange it relative to the hose, which source of interference transmits the vibrations originating from the motor vehicle in an amplified manner to the hose. In order to cause a pressure fluctuation, the hose is deformed locally at the site of the interference source. In this case, the source of the interference does not have to be of an active nature, for example, be constructed in the form of a compressor or of an actuator. In contrast, for reasons of cost, passively acting interference sources, such as mass-type bodies, are preferable, which transmit only one vibration caused by the motor vehicle in an amplified manner to the hose in order to artificially cause the measurable pressure fluctuation required for detection purposes.
It is advantageous for the interference source to be arranged or constructed such that the latter is excited by the vibrations originating from the motor vehicle to perform a movement in the direction of the vertical axis of the motor vehicle. As a result, the gravitational force can advantageously be utilized for intensifying the pressure fluctuation occurring in the hose. In this case, the interference source is advantageously arranged in the direction of the gravitational force above and below the hose. In particular, the device can be implemented in a constructively simple manner if the interference source leads to a compressing of the hose for causing a pressure fluctuation. Depending on the local situation, the excitation may also take place in a direction deviating from the vertical line.
It is also advantageous for the interference source to be arranged in the center between the two ends of the hose. This variant is particularly advantageous in the case of pressure sensors provided at both ends of the hose because the pressure fluctuation then has to be perceived equally by both sensors.
In principle, for reasons of a precise detection, it is advantageous for the sensor system to have two pressure sensors that are arranged at the two opposite ends of the hose, which sensors close off the hose. In this case, it is possible to mutually correlate the signals supplied by the two pressure sensors. The detection precision can thereby be increased—even in the case of only slight pressure fluctuations.
As described above, it is advantageous for the interference source to be a mass-type body. The latter can be fastened, for example, to the exterior surface of the hose. Its weight can define in a simple manner which pressure fluctuations are caused in the case of which external interference in the pressure hose system. The suitable mass can be determined by experimenting because this mass may be dependent on the design of the chassis.
A further improvement of the diagnosis of the sensor system can be achieved in that the device includes an acceleration sensor, particularly a chassis sensor system which provides a time-dependent acceleration signal that can be processed for a qualitative evaluation of the pressure signal by the evaluating unit. Advantageously, such acceleration sensors are already available in vehicles so that only the acceleration values supplied by this sensor have to be linked in the evaluating unit with the signals supplied by the pressure sensors.
For example, by use of the acceleration sensors, accelerations caused as a result of an unevenness of the ground or of potholes are detected (in the direction of the vertical axis of the vehicle, i.e. of the z-axis). These significant accelerations in the z-axis direction also become noticeable as an interference in the hose of the sensor system. In the case of an appropriate operability of the sensor system, in the event of the occurrence of such acceleration signals, pressure signals of the pressure sensors representing pressure fluctuations also have to be detected in the evaluating unit. If this is so, a conclusion can be drawn on an appropriate functioning of the pressure hose system.
However, if such a time-related correlation does not exist, there may be a malfunctioning of the pressure hose sensor system. By means of other sensor system data, particularly acceleration values, the data supplied by the pressure sensors can thereby be made plausible. Likewise, it is contemplated to include the data made available by other sensors for the extraction of pressure fluctuations caused by an interference.
All information required for the diagnosis of the sensor system can be processed in a single evaluating unit, for example, an airbag control device. The invention can therefore advantageously be implemented by the corresponding adaptation of the software for the evaluating unit and can be provided in a cost-effective manner.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.